The invention relates to a propulsion system for ships, in particular for cruise vessels.
It is known to choose propulsion arrangements for ships, preferably for cruise/passenger vessels which make available the forces necessary for the ahead course as well as the transverse forces necessary for steering the ships during manoeuvres and/or for keeping the course in the stern area for constituting the steering moment around the vertical axis by corresponding control or regulating signals which act on the respective electro hydraulic steering gear/adjusting unit for the propulsion arrangement over a corresponding torsion about the respective system vertical axis.
For maintaining a most possible straight course of ships for long distance sailing, it is necessary to adjust the whole main drive or for twin propeller ships at least one of the two drives about the vertical axis so that a very small angle is obtained in the shortest time This is the only way to economically produce the transverse forces necessary for maintaining the straight forward traveling of the ship. In particular for cruise vessels, ship driving elements, known as podded propulsors, are used for which the drive, such as for example the electrical motor, the propeller and the gondel, are combined in an unit as a rotatable suspension which is placed outside the proper hull. The range of application of these podded propulsors concerns in particular ship types which are particularly appropriate for the diesel electric propulsion, such as for example passenger vessels or ice breakers, and particularly where a good manoeuvrability is necessary. Two systems are used presently for these podded propulsors. First, the single propeller with a separate excited electrical motor and air cooling and second, the tandem propeller with a permanently excited electrical motor and cooling of the housing. For single propellers, the differentiation is made between the thrust arrangement for which the propeller is placed behind the turning axis and the pull arrangement (propeller in front of the turning axis). All the podded propulsors have in common that at least one propeller and its drive are placed in a turnable gondel-type unit.
Inside such a combined main and control drive, i.e. for such podded propulsors, for long distance travelling the whole inert masses around the turning axis are to be accelerated and to be braked again purposefully for the precalculated small adjusting angle in order to be able to achieve a stable operation of the control circuit for the straight forward behaviour of the ship. This results in that, for the numerous course correction forces or steering moments required for the ship, it must be reached that the ship to steer avoids as far as possible additional movements around its vertical axis for an economical operation The lifetime of the bearing of the main and control drives integrated into the ship in the preferably high dynamically loaded small angle area is reduced in case of such an operation to the zero position and the valves, relays, switches and components required inside the system for the hydraulic adjustment around the vertical axis as well as the shipbuilding constructions for the integration of the podded propulsors are exposed to heavy wear which results from the system dynamics and from the lower fatigue strength under reversed stresses. The systems used for the safety and economy of such driven and/or controlled ships are very time-consuming and very expensive in case of care, maintenance and repair works since the elements and components are of difficult access what makes necessary in most of the cases a docking—which is not economical for the operator of the ship—with a corresponding loss of use.